In recent years, soft silicone hydrogel contact lenses, for example, Focus NIGHT & DAY™ and O2OPTIX™ (CIBA VISION), and PureVision™ (Bausch & Lomb) become more and more popular because of their high oxygen permeability and comfort. “Soft” contact lenses conform closely to the shape of the eye, so oxygen cannot easily circumvent the lens. Soft contact lenses must allow oxygen from the surrounding air (i.e., oxygen) to reach the cornea because the cornea does not receive oxygen from the blood supply like other tissue. If sufficient oxygen does not reach the cornea, corneal swelling occurs. Extended periods of oxygen deprivation cause the undesirable growth of blood vessels in the cornea. By having high oxygen permeability, a silicone hydrogel contact lens allows sufficient oxygen permeate through the lens to the cornea and to have minimal adverse effects on corneal health.
However, a silicone hydrogel material typically has a surface or at least some areas of its surface which is hydrophobic (non-wettable). Lipids or proteins from the ocular environment can be adsorbed onto hydrophobic surface or surface areas of a silicone hydrogel contact lens. The hydrophobic surface or surface areas of a silicone hydrogel contact lens may cause it be adhered to the eye. Thus, a silicone hydrogel contact lens will generally require a surface modification to increase surface hydrophilicity.
A known method for modifying the hydrophilicity of a relatively hydrophobic contact lens material is a layer-by-layer (LbL) polyionic (or polyelectrolyte) material deposition technique (see for example, U.S. Pat. Nos. 6,451,871, 6,717,929, 6,793,973, 6,884,457, 6,896,926, 6,926,965, 6,940,580). LbL coatings may provide high hydrophilicity and lubricity to contact lenses and thereby enhance wearer's comfort and/or ocular health. Although this technique can provide a cost effective process for rendering a silicone hydrogel material wettable, it may require relatively long time and laborious steps to apply an LbL hydrophilic coating which can impart hydrophilicity and lubricity to a silicone hydrogel contact lens. Moreover, an LbL coating process generally is carried out at very low pH (e.g., below pH 4) or at very high pH (e.g., above pH 9), and as such, one or more additional post-coating processes are needed to neutralize pH before each coated lens can be placed in a packaging saline at a pH of about 7 in a package. Such additional post-coating processes may decrease the production efficiency and increase the production cost.
Therefore, there is still a need for methods of efficiently applying a hydrophilic coating to a silicone hydrogel contact lens.